1. Field of the Invention
The present invention relates generally to prosthetic hearing devices, and more particularly, to an implantable interferometer microphone which may be utilized in prosthetic hearing devices.
2. Related Art
In recent years, rehabilitation of sensorineural hearing disorders with prosthetic hearing devices has acquired major importance. Such hearing disorder include, for example, various types of inner ear damage through complete postlingual loss of hearing or prelingual deafness, combined inner ear and middle ear damage, and temporary or permanent noise impressions (tinnitus).
Particular effort has been directed to providing some hearing capability to those persons for which hearing has completely failed due to accident, illness or other effects or for which hearing is congenitally non-functional. If, in such patients, only the inner ear (cochlea), and not the neural auditory path which leads to the brain, is impaired, the remaining auditory nerve may be stimulated with electrical stimulation signals to produce a hearing impression which can lead to speech comprehension. In these so-called cochlearm implants (also referred to as Cochlear™ devices, Cochlear™ implant systems, and the like; “cochlear implants” herein), an array of stimulation electrodes is inserted into the cochlea. This array is controlled by an electronic system which typically is surgically embedded as a hermetically sealed, biocompatible module in the bony area behind the ear (mastoid). The electronic system essentially contains a decoder and driver circuitry for the stimulation electrodes. Acoustic sound reception, conversion of the sound into analog electrical signals, and the processing of the analog signals, typically takes place in a so-called sound processor which is typically worn outside on the recipient's body. The sound processor superimposes the preprocessed signals, properly coded, on a high frequency carrier signal which, via inductive coupling, is transmitted (transcutaneously) to the implanted circuitry through the closed skin. In the above and other conventional prosthetic hearing devices, the sound-receiving microphone is also located outside of the recipient's body. In most conventional prosthetic hearing devices, the microphone is located in a housing of a behind-the-ear (BTE) component worn on the external ear, and is typically connected to the sound processor by a cable.
For some time there have been approaches to treat sensorineural and conducive hearing losses using totally implantable hearing aids. Such prosthetic hearing devices may offer better rehabilitation than conventional hearing aids. A common approach in such devices is to stimulate an ossicle of the middle ear or, directly, the inner ear, via mechanical or hydromechanical stimulation rather than via an amplified acoustic signal as in conventional hearing aids, or electrically, as in cochlear implants. The actuator stimulus of these systems is accomplished with different physical transducer principles such as, for example, by electromagnetic or piezoelectric technologies. The advantage of these devices is seen mainly in a sound quality which is improved compared to that of conventional hearing aids. Such totally implantable electromechanical hearing aids are described, for example, by H. P. Zenner et al. “First implantations of a totally implantable electronic hearing system for sensorineural hearing loss”, in HNO Vol. 46, 1998, pp. 844-852; H. Leysieffer et al. “A totally implantable hearing device for the treatment of sensorineural hearing loss: TICA LZ 3001”, in HNO Vol. 46, 1998, pp. 853-863; and H. P. Zenner et al. “Totally implantable hearing device for sensorineural hearing loss”, in The Lancet Vol. 352, No. 9142, page 1751.
Another type of totally implantable prosthetic hearing device is the bone anchored hearing aid (BAHA). BAHA is a surgically implantable system for treatment of hearing loss through direct bone conduction. It has been used as a treatment for conductive and mixed hearing losses as well as for the treatment of unilateral sensorineural hearing loss. Typically, BAHA is used to help people with chronic ear infections, congenital external auditory canal atresia and single sided deafness, as such persons often cannot benefit from conventional hearing aids. Such systems are surgically implanted to allow sound to be conducted through the bone rather than via the middle ear.
More recently, totally implantable cochlear implants have been developed for use alone or in combination with other technologies, such as the noted totally implantable hearing aid.
One challenge of implantable prosthetic hearing systems, particularly those that are substantially or totally implantable, is the use of a totally-implantable microphone. Some of the problems encountered with implantable microphones include difficulty optimizing the coupling of sound between the tissue and the device, size restrictions due to the space available in the target implant location such as the middle ear, and the need to deliver sufficient gain to aid severe hearing loss.